The invention relates to an improvement on U.S. Pat. No. 4,801,126 “Hydraulically operated lift mechanism”. This patent includes a three chamber cylinder that allows for the use of one chamber as a gas accumulator acting as a phantom counterweight for vertical Industrial hoisting and artificial lift pumping applications.
This mentioned patented invention has been successfully applied for artificial lift on the oil and water pumping industries, among others. It has done so with 10% of the weight of the classic equivalent Beam pump, and less than 50% energy consumption per barrel of fluid extracted.
However, when applications of the mentioned patent use the triple cylinder with the plunger pointing up, which is the case for artificial lift, the gas chamber ends being situated at the lower part of mentioned cylinder. It is very difficult to stop a migration of gas to the up chamber, not having the possibility to bleed the gas from the hydraulic oil, creating a much lower life for the cylinder and several maintenance issues. This use is a 24/7 application, totaling 8760 hours a year, a major engineering challenge.
This application entails the conversion of the triple cylinder gas chamber to contain now oil instead of gas. That former gas chamber will now be connected to an independent accumulator (gas over oil), whereas now the gas is above the oil instead of below, avoiding in this manner any migration of gas to the oil. A small third pump is now able to replenish the oil lost or the system can bleed this new oil chamber that no longer contains gas.
This new arrangement creates other major improvements:                When a loss of load occurs (wire rope broken, rod parted) the present solution closes a ball valve that connects the large accumulator to the triple cylinder. No matter how fast this ball valve closes, a volume of pressurized gas stays in the cylinder launching the plunger at a very high speed to the end stop. On the new arrangement, when the load is lost, a check valve closes the oil connection to the triple cylinder, with a minimum energy left, hence avoiding the launching of the plunger.        In artificial lift, when a pump stops, normally the rod load will change as time passes. In the older design of the triple cylinder, when that occurs, the position of the plunger changes due to the gas still in the cylinder, this gas will force a changed position when the load changes. This new arrangement will maintain the same position of the rod, no matters what occurs with the load.        When, during servicing the unit, it is necessary to descend the plunger, the present technology makes this task difficult due to the rebounding of the plunger containing gas. As the new design has no gas, the annoying rebounding disappears.        All seals of the triple cylinder are now under oil, making a leak far less important and increasing the life of the cylinder many times over, and at the same time eliminating many maintenance problems.        
In one of the preferred designs, one or more matrix variable frequency drive (MVFD) designed for real four quadrant applications is used, able to return power to the grid with very high efficiency. This feature is indispensable as a vertical pumping movement has always energy generating parts of a cycle which is, with today's technology, energy lost. This device new MVFD has the added advantage to eliminate the harmonics on the power lines, a major problem with a standard VFD for the power companies.
In another design version, the prime mover, instead of an electric motor uses an engine propelled by the casing gas of the well itself. This application is very well suited to this design as a triple cylinder has a very low kinetic energy content, compared with a typical Beam pump, and the engine does no longer have the heavy kinetic load of the old design.
In another design version, a fixed speed electrical motor is attached to an over center swash plate pump/motor. The pump controls now the direction of the flow, the accelerations and decelerations as well as the speed. This set up eliminates the nasty frequencies created by variable frequency drives, and is also able to motor as well as generate power back to the grid.